SAT-117 Caught in a NET: Is the Female Reproductive Tract a Sex Specific Site for Anti-Citrullinated Protein Antibodies?

Abstract Disclosure: A.O. Sequoia: None. R.A. Horne: None. K. Franckowiak: None. M. Corbitt: None. H.M. Rothfuss: None. M. Demoruelle: None. B.D. Cherrington: None. Women have a three-fold higher rate of rheumatoid arthritis (RA) as compared with men, and several reproductive factors are correlated with the increased risk of RA in women. RA autoimmunity can develop when citrullinated (cit) proteins are generated at a mucosal surface by peptidylarginine deiminase (PAD) enzymes, which post-translationally covert arginine to a non-coded citrulline residue in target proteins. Auto-antibodies to cit-proteins, termed anti-citrullinated protein antibodies (ACPAs), are produced in the mucosa, but can become systemic and trigger joint inflammation. Prior studies have established the association between PAD4 mediated neutrophil extracellular traps (NETs) which generate cit-proteins and ACPA in the sera of RA patients, while other work has localized NETs to mucosal surfaces, including in the female reproductive tract (FRT). Shared mucosal sites (ie. lung, gingiva, and gastrointestinal tract) have yet to explain the sex disparity in RA, leading us to hypothesize that the FRT mucosa is a sex specific site of NET generation and ACPA production. To begin to test our hypothesis, we first examined whether PAD enzymes and cit-fibrinogen are present in FRT fluid (FRT-F) during the mouse estrous cycle. Our results demonstrate that PAD enzymes and cit-fibrinogen levels fluctuate in wild type mouse FRT-F during the estrous cycle in parallel with PAD enzymatic activity. These results are similar to our previous work showing that in FRT-F from women, ACPA levels and PAD activity peak at day 5 of the menstrual cycle, just post-menses. The FRT can locally produce antibodies, prompting us to next test whether ACPA to cit-fibrinogen and NET associated proteins are present in FRT-F across the estrous cycle. Our results show that not only are ACPA and NET associated proteins highest during metestrus, but NETs are also visible via confocal microscopy in FRT-F. We are currently using mass spectrometry to identify the mouse FRT citrullinome during the different stages of the estrous cycle. Ultimately, our objective is to identify the mechanism by which ACPA are produced in the FRT and to identify possible targets for sex-specific diagnostic tests or treatments to improve clinical outcomes for women suffering from RA. Presentation: Saturday, July 12, 2025